In an ordinary photographic or diffusion transfer process, it is known that a temporary barrier layer may be provided between layers in a photographic element into which a processing solution penetrates. Particularly in the diffusion transfer photographic process, a neutralizing layer may be used for the purpose of stopping development, stabilizing the image, or like purposes. It is also well known in the art that a temporary barrier layer may be used for the purpose of "timing" the neutralization to prevent the neutralization of a developing solution by the neutralizing layer from proceeding earlier than required and hence prevent the reduction of the maximum density. Such a temporary barrier layer used for this purpose is called a timing layer. Examples of such a timing layer are disclosed in U.S. Pat. Nos. 4,061,496, 4,056,394, and 4,201,587, and Japanese Patent Application (OPI) Nos. 72622/78 (corresponding to U.S. Pat. No. 4,199,362), and 141644/82 (the term "OPI" as used herein means an "unexamined published application").
In general, the development reaction in a silver halide photographic process proceeds slowly at a low temperature but more rapidly at an elevated temperature. Therefore, if the diffusion transfer process is used for instant photography where development is conducted at various temperatures, unlike ordinary photography where development is conducted at a controlled temperature, it is extremely important to impart to the photographic element a function of compensating for development speed by causing the neutralization reaction of the processing solution to depend on the temperature by accelerating the neutralization reaction at an elevated temperature or slowing the neutralization reaction at a low temperature in order to obtain a consistently excellent image regardless of change in development temperature. The above listed patents discribe many examples of timing layers having such a temperature compensation effect.
A so-called monosheet type diffusion transfer photographic process is subject to a problem of a rise in the color density over the maximum density portion, gradation portion, and minimum density portion with the passage of time (several days to weeks) after the formation of an image. This is a phenomenon called "aftertransfer" which remarkably deteriorates the picture quality. In this phenomenon, a dye released during the processing step is not entirely allowed to migrate to a mordant layer, and part of the dye is left in layers other than the mordant layer. The dye left in the other layers gradually migrate into the mordant layer with the passage of time. The cover sheet containing a timing layer as described in the above cited patents has virtually no effect on inhibiting such an aftertransfer phenomenon. Even if the cover sheet has somewhat of an effect, there is an attendant disadvantage in that the sharpness of the transfer image is deteriorated.
Japanese Patent Application (OPI) No. 19137/85 made it possible to inhibit aftertransfer without deteriorating sharpness by using a photographic element. Particularly, in a color diffusion transfer photographic element containing a neutralizing system for lowering the pH of an alkaline processing solution, the processing solution neutralizing process in the neutralizing system is divided into two stages. This neutralizing system comprises a neutralizing layer and a timing layer. This timing layer is directly or indirectly laminated on or under the neutralizing layer in such a positional relationship that alkaline processing solution reaches the neutralizing layer via the timing layer. Different neutralizing processes proceed at the two stages. More particularly, the photographic element disclosed in Japanese Patent Application (OPI) No. 19137/85 is characterized by the neutralization process which proceeds by at least two stages such that in the first stage the development and dye release reaction is interrupted due to the lowering of the pH of the processing solution (photographic system) while at the same time the transfer of a dye for forming a transfer image can still continue, and in the second stage of pH of the processing solution (photographic system) is gradually lowered to a final value at which dye transfer is also inhibited and which is capable of withstanding prolonged storage, as a result of which the dye remains immobilized and the image remains stable. One such neutralizing process is characterized by a rapid pH change. This is a so-called "inverted S-shaped" pH drop process in which pH is maintained at a high value for some period of time, and then shows a rapid drop. Another neutralizing process is characterized by a relatively slow pH drop. However, the latter process may also be an inverted S-shaped pH drop process. Such a twostage neutralizing process can be accomplished by sequentially coating on a support a neutralizing layer, a 2nd timing layer, an auxiliary neutralizing layer, and a 1st timing layer to provide a neutralizing system layer. Or by using a neutralizing layer which makes a gradual neutralization, such a two stage neutralizing process can also be accomplished by sequentially coating on a support a neutralizing layer, an auxiliary neutratizing layer, and a 1st timing layer, without using a 2nd timing layer.
Such a pH drop process (mode) can be freely controlled particularly by adjusing the component, composition and coated amount of the above described timing layer. That is, the duration (x) during which pH is maintained high can be controlled by the first timing layer, the pH drop at the first stage can be controlled by the auxiliary neutralizing layer, and the pH drop process after the period x can be controlled by the second timing layer and the neutralizing layer. Aftertransfer can be effectively controlled by properly controlling this neutralizing process. The greater the temperature coefficient of the 1st timing layer is, i.e., the lower the temperature the longer timing provides the 1st timing layer. In other words, the timing layer preferably has an effect of retarding neutralization.
On the other hand, U.S. Pat. No. 4,356,249 describes an improvement in the processing temperature dependence of a color diffusion transfer photographic film unit (assemblage) containing a positive type redox compound as a dye image forming compound. In accordance with this U.S. patent, this improvement can be accomplished by providing two layers, i.e. a 1st timing layer and a 2nd timing layer, and further providing two neutralizing layers, i.e. a conventional neutralizing layer and an auxiliary neutralizing layer between the 1st timing layer and the 2nd timing layer. (The first timing layer has a negative temperature coefficient.) In such a photographic system, the auxiliary neutralizing layer is designed to inhibit the release of a dye from a positive type redox compound involved in the development of silver halide more at a low temperature than at an elevated temperature in order to improve the processing temperature dependence thereof. Thus, this photographic system is not intended to prevent aftertransfer of a diffusive dye released from a positive type redox compound. Therefore, this photographic system cannot provide an effect of preventing aftertransfer.
When stored at a high temperature and high humidity, the image formed by processing may be gradually discolored even in a dark place, causing a remarkable deterioration of the picture quality. Particularly, a magenta dye image is susceptible to such a discoloration due to its structure. On the other hand, the above described aftertransfer causes color intensification. Actually, such color intensification and discoloration compensate each other and thus cannot be noticeably observed. However, if the neutralizing system disclosed in Japanese Patent Application (OPI) No. 19137/85 is used to inhibit aftertransfer, discoloration is noticeably observed rather than color intensification. Therefore, if such a neutralizing system is stored at a high temperature and a high humidity, the picture quality is deteriorated.
Accordingly, if this neutralizing system could be improved in the image preservability, a complete system free of both color intensification and discoloration can be obtained.